The invention relates to a surge arrester having at least one dissipation element, which is arranged between two electrically conductive end fittings, and having at least one bracing element, which is attached to the two end fittings and, in the axial direction, holds together the stack formed from the dissipation element and the end fittings.
A surge arrester such as this is known, for example, from Japanese Patent Application No. 62/149511.
In that document, a number of dissipation elements are combined to form a cylindrical stack, which also has an end fitting at each of its ends, with the end fittings having recesses for bracing elements in the form of rods. The bracing elements are braced between the end fittings by means of threaded nuts, with the threaded nuts resting on the edges of the recesses of the end fittings.
When assembling such a surge arrester, the individual nuts must be screwed tight, and a uniform pressure distribution should be ensured on the circumference of the end fittings.
The present invention is based on the object of simplifying the assembly process and of reliably bracing the stack for a surge arrester of the type mentioned initially.
According to the invention, the object is achieved in that the bracing element is held in a bracing sleeve in at least one end fitting, in that the external contour of the bracing sleeve tapers conically in the axial direction toward the center of the stack in a conical region, in that the bracing sleeve has a hole for holding a bracing element, the boundary walls of which hole can move toward the interior of the hole at least in the conical region, and in that the end fitting has a recess passing through it, for holding in each case one clamping sleeve, into which recess the respective clamping sleeve can be at least partially pushed, with the conical region being deformed.
For attachment to the end fitting, the bracing element can be pushed into the bracing sleeve, which is then inserted into the recess passing through it, within the end fitting. The already assembled stack is then fixed, and a tensile stress is applied to the bracing element. This elastically lengthens the bracing element. The spring stress in the bracing element is stored by at least one spacer in the stack compensating for the bracing movement. Such a spacer may be provided, for example, by a spacing screw which can move between an end fitting and the dissipation elements. The bracing sleeve can be pushed into the recess passing through the end fitting until the conical region of the bracing sleeve abuts against the walls of the recess passing through the end fitting, so that the boundary walls start to move radially toward the hole interior onto the bracing element.
This further deforms the conical region of the bracing sleeve, and the boundary walls are pressed radially inward onto the bracing element. The bracing element is thus held in the bracing sleeve by a force fit. To do this, the dimensions and shapes of the recess passing through the end fitting and of the bracing sleeve must be appropriately matched to one another. The conicity of the bracing sleeve must likewise be suitably configured.
The bracing element advantageously consists of a fiber-reinforced epoxy resin. The radial introduction of force into the bracing element by means of the force fit with respect to the bracing sleeve firstly results in there being no notch effect on the bracing element while, secondly, virtually the entire cross section of the bracing element is used to transmit the axial force. The axial bracing of the stack automatically holds the bracing element in the bracing sleeve.
It is advantageously possible to provide for the recess passing through the end fitting to be designed to be complementary to the conical region of the bracing sleeve.
This means that it is particularly simple to compress the bracing sleeve in the desired manner while exerting axial tension toward the bracing element.
Furthermore, it is advantageously possible to provide for the bracing sleeve to be slotted in the conical region, so that the boundary walls of the hole can move in a radially sprung manner in the conical region.
The slotting in the bracing sleeve makes it particularly simple for the boundary walls of the hole to move radially in the bracing sleeve.
A further advantageous refinement of the invention provides for the bracing element to be held by means of a bracing sleeve in each of the end fittings.
It is also advantageously possible to provide for a number of bracing elements to be provided, parallel to the axis of the stack, on its external circumference.
This makes it possible to distribute the large axial forces in the dissipation stack well between a number of bracing elements. The uniform distribution of the tensile forces between the various bracing elements is produced automatically. Furthermore, the use of a number of bracing elements results in greater mechanical strength.
It is also advantageously possible to provide for the end fittings to project radially beyond the dissipation elements and, in the projecting region, to have conical holes for holding the respective bracing sleeves.
In this way, the bracing elements can be used to form a cage which surrounds the dissipation elements and which, for example, can be encapsulated with a silicone elastomer, together with the dissipation elements, while the surge arrester is being manufactured.
In addition, it is advantageously possible to provide for each bracing sleeve to have a hole whose shape is designed to form an accurate fit with the external contour of the respective bracing element.
This allows a particularly effective force fit to be achieved between the respective bracing sleeve and the bracing element.